The present invention relates to a thermo-actuator, and more particularly to a thermo-actuator provided in a wax-pellet thermostat for automotive engines and various thermo-sensors.
The thermo-actuator in the wax-pellet thermostat includes a steel rod secured to a housing at a base end thereof, a guide member slidably mounted on the rod, a seal spool secured to the guide member and provided around the rod, a heat conductive cylinder secured to the guide member and exposed to a coolant, a wax provided in the cylinder, and a spring urging the guide member towards the base end of the rod.
When the temperature of the coolant rises in excess of a predetermined value of the thermostat, the wax expands. This forces the seal spool against the steel rod. As the wax squeezes the seal spool around the rod, the cylinder moves outwardly together with the guide member against the spring, thereby opening a valve. When the thermostat cools, the wax contracts, so that the seal spool expands, and the cylinder is moved to the base end of the rod by the spring.
In an ordinary thermostat having a valve opening lift of 10 mm, the pressure of the wax for lifting the valve becomes very high as 102 kg/cm.sup.2. To resist the high pressure and to ensure the durability, the seal spool is made to have a large thickness, for example 45% of the diameter of the rod. Therefore, in order to squeeze and deform the thick and stiff seal spool, a large force of 30 kg/cm.sup.2 for 102 kg/cm.sup.2 is consumed. In addition, there occur troubles, such as wear and tear of the seal spool, and sticking of the spool to the rod, because of large friction.